1. Field of the Invention
The present invention relates to a method of manufacturing a substrate over which a semiconductor layer is provided with an insulating layer therebetween, and particularly relates to a method of manufacturing a silicon on insulator (SOI) substrate. Further, the present invention relates to a method of recycling a bond substrate in the manufacturing method of an SOI substrate.
2. Description of the Related Art
As substrates suitable for manufacture of semiconductor devices that achieve low power consumption and high-speed operation, attention has been directed to SOI substrates in which a semiconductor layer is provided over a base substrate having an insulating surface.
One of known methods of manufacturing an SOI substrate is a hydrogen ion implantation separation method (see Patent Document 1). The hydrogen ion implantation separation method is a technique of forming an SOI substrate in the following manner. An oxide film is formed on one of two silicon wafers which is to serve as a bond substrate. At the same time, by implanting hydrogen ions into the bond substrate, a microbubble layer is formed in the bond substrate. The bond substrate is put in close contact with the other silicon wafer that is to serve as a base substrate, with the oxide film therebetween. Then, by a heat treatment, the bond substrate is split with the use of the microbubble layer as a splitting plane. Another heat treatment on the base substrate side forms a strong bond between the base substrate and a semiconductor layer that is split from the bond substrate. Thus, an SOI substrate is formed.
Furthermore, for an efficient and economical use of silicon wafers, a method by which many SOI substrates can be manufactured with as few silicon wafers as possible has been researched (see Patent Document 2).
[Reference]
[Patent Document]
    [Patent Document 1] Japanese Published Patent Application No. H5-211128    [Patent Document 2] Japanese Published Patent Application No. 2000-349266
The bond substrate still retains its wafer form after the split. If defects and the like remaining on a surface used for the split are removed by etching, polishing, or the like, the bond substrate can be reused to manufacture another SOI substrate.
Repeated use of a bond substrate in this manner has involved a problem of an increase in oxygen defects such as an oxidation-induced stacking fault (OSF) due to an ion irradiation step, thermal history during split of the bond substrate, or the like. If a bond substrate having an increased number of oxygen defects is used to manufacture an SOI substrate, semiconductor properties significantly deteriorate.
Further, in an ion irradiation step, an impurity element such as a heavy metal which is contained in an electrode, a chamber, or the like could be added to the bond substrate. Like oxygen defects, such an impurity element adversely affects the semiconductor properties.